1. Field of the Invention
This invention relates to the preparation of copolyamides and is particularly concerned with copolyoxalamides.
2. Description of the Prior Art
Polyamide polymers are well known to those skilled in the art, see for example The Encyclopedia of Polymer Science and Technology, Vol. 10, pp. 347-593, 1969, Interscience Publishers, New York, N.Y. The various kinds of repeating units disclosed therein which are linked by the carbonamide group ##STR3## determine the variation in physical properties observed for the different types of polyamides. Physical properties like melting point and solubility are dependent on the type of repeating unit employed.
Polyoxalamides wherein the carbonyl groups are derived from the oxalyl radical are particularly dependent on the type of radical derived from the diamine monomer unit for the properties they display. For example poly(hexamethyleneoxalamide) melts at 320.degree. C. which is prohibitively high for this material to be practically useful as an injection moldable material. On the other hand, poly(decamethyleneoxalamide), which differs from the former material by only four carbon atoms in the chain separating the two amide nitrogens, melts at the very much lower value of 240.degree. C. and has a low Tg because of its aliphatic backbone.
Various kinds of polyoxalamides are known in the art. Generally speaking, they are high melting, difficult to process, crystalline materials. Illustratively, U.S. Pat. No. 2,977,340 discloses fiber forming polyoxalamides wherein a divalent aliphatic radical connects the oxalamide residues. U.S. Pat. No. 2,945,011 shows copolyoxalamides wherein the radicals separating the oxalamide residues alternate between an aromatic radical and an aliphatic radical containing from 4 to 15 carbon atoms which preferably contain at least one ether linkage. The copolyoxalamides can be used for the production of fibers, coatings, and molded objects.
U.S. Pat. No. 3,553,289 discloses polyoxalamides wherein the oxalamide residues are separated by the aliphatic radical derived from 3-aminomethyl-3,5,5-trimethylcyclohexylamine. The use of additional diamines in conjunction with the cyclohexyl compound is also disclosed. However, specific aromatic diamines are not disclosed and the only working example showing a mixture calls for a mixture of 9 percent hexamethylene diamine and 91 percent 3-aminomethyl-3,5,5-trimethycyclohexylamine. The polyoxalamides are then blended with other polyamides to be spun into synthetic fibers.
U.S. Pat. No. 3,932,365 discloses both poly(p-phenyleneoxalamide) fibers and poly(4,4'-methylenebisphenyleneoxalamide) fibers and British Pat. No. 1,451,680 discloses a series of polyoxalamide-amide polymers used primarily for fiber making.
The prior art does not disclose a polyoxalamide which could serve as a high temperature resistant engineering thermoplastic, that is to say, a polyoxalamide that is injection moldable yet is still possessed of good high temperature resistance.
We have found that the novel copolyoxalamides prepared in accordance with the present invention and described in detail hereinbelow are characterized by injection moldability and by remarkable resistance to a high temperature environment including excellent resistance to oxidative degradation.